Certain aeronautic vehicles, for example aeroplanes such as the ATR-72 and ATR-42, do not always include an Auxiliary Power Unit (APU). Such aeronautic vehicles use hotel mode for ground operations. In hotel mode, one engine (which is distinct from an APU at least in that it is an engine capable of providing propulsion) runs in a low power mode. Where the engine is a turboprop engine the propeller is decoupled from the engine by a propeller brake, for example. A problem with such an arrangement is that the environmental control system (ECS) may not provide enough cooling capacity whilst the engine is operating in this low power mode. A prior art solution to this problem is to increase the cooling power by providing an additional vapour cycle cooling system as part of the aeronautic vehicle. This can result in a considerable increase in the complexity and weight of the aeronautic vehicle.
It is a non-exclusive object of the invention to alleviate the above mentioned problems.